Solar batteries have become popular to suppress use of fossil fuel and to reduce environmental loading. For example, a solar battery installed on the roof of a house can be an electric power source of various electric products in the house, and can charge an electric vehicle or a plug-in hybrid vehicle. Consequently, users want to know how much power the solar battery generates, and how much of the power consumption of the house is covered by the generated power; and there are known conventional technologies that display power generation amounts on display units placed in houses (see, for example, Patent Document 1).
Incidentally, as plug-in hybrid vehicles and electric vehicles have become popular, vehicles tend to have the solar power generation systems installed. For a solar power generation system in a vehicle, passengers also want to know how much the current power generation amount is. Therefore, technologies have been under investigation that display power generation amounts on meter panels or displays.